Buggy code:
public class URLRewritingModifier extends AbstractTestElement implements Serializable , PreProcessor { private static final String SEMI_COLON = ";" ; private transient Pattern pathExtensionEqualsQuestionmarkRegexp ; private transient Pattern pathExtensionEqualsNoQuestionmarkRegexp ; private transient Pattern parameterRegexp ; private transient Pattern pathExtensionNoEqualsQuestionmarkRegexp ; private transient Pattern pathExtensionNoEqualsNoQuestionmarkRegexp ; private static final String ARGUMENT_NAME = "argument_name" ; private static final String PATH_EXTENSION = "path_extension" ; private static final String PATH_EXTENSION_NO_EQUALS = "path_extension_no_equals" ; private static final String PATH_EXTENSION_NO_QUESTIONMARK = "path_extension_no_questionmark" ; private static final String SHOULD_CACHE = "cache_value" ; private transient String savedValue = "" ; public void process ( ) { } private void modify ( HTTPSamplerBase sampler , String value ) { } public void setArgumentName ( String argName ) { } private void initRegex ( String argName ) { String quotedArg = Perl5Compiler . quotemeta ( argName ) ; pathExtensionEqualsQuestionmarkRegexp = JMeterUtils . getPatternCache ( ) . getPattern ( ( ( ( URLRewritingModifier . SEMI_COLON ) + quotedArg ) + "=([^\"\'>&\\s;]*)[&\\s\"\'>;]?$?" ) , ( ( Perl5Compiler . MULTILINE_MASK ) | ( Perl5Compiler . READ_ONLY_MASK ) ) ) ; pathExtensionEqualsNoQuestionmarkRegexp = JMeterUtils . getPatternCache ( ) . getPattern ( ( ( ( URLRewritingModifier . SEMI_COLON ) + quotedArg ) + "=([^\"\'>&\\s;?]*)[&\\s\"\'>;?]?$?" ) , ( ( Perl5Compiler . MULTILINE_MASK ) | ( Perl5Compiler . READ_ONLY_MASK ) ) ) ; pathExtensionNoEqualsQuestionmarkRegexp = JMeterUtils . getPatternCache ( ) . getPattern ( ( ( ( URLRewritingModifier . SEMI_COLON ) + quotedArg ) + "([^\"\'>&\\s;]*)[&\\s\"\'>;]?$?" ) , ( ( Perl5Compiler . MULTILINE_MASK ) | ( Perl5Compiler . READ_ONLY_MASK ) ) ) ; pathExtensionNoEqualsNoQuestionmarkRegexp = JMeterUtils . getPatternCache ( ) . getPattern ( ( ( ( URLRewritingModifier . SEMI_COLON ) + quotedArg ) + "([^\"\'>&\\s;?]*)[&\\s\"\'>;?]?$?" ) , ( ( Perl5Compiler . MULTILINE_MASK ) | ( Perl5Compiler . READ_ONLY_MASK ) ) ) ; <START_BUG> parameterRegexp = JMeterUtils . getPatternCache ( ) . getPattern ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( "[;\\?&]" + quotedArg ) + "=([^\"\'>&\\s;]*)[&\\s\"\'>;]?$?" ) + "|\\s[Nn][Aa][Mm][Ee]\\s*=\\s*[\"\']" ) + quotedArg ) + "[\"\']" ) + "[^>]*" ) + "\\s[vV][Aa][Ll][Uu][Ee]\\s*=\\s*[\"\']" ) + "([^\"\']*)" ) + "[\"\']" ) + "|\\s[vV][Aa][Ll][Uu][Ee]\\s*=\\s*[\"\']" ) + "([^\"\']*)" ) + "[\"\']" ) + "[^>]*" ) + "\\s[Nn][Aa][Mm][Ee]\\s*=\\s*[\"\']" ) + quotedArg ) + "[\"\']" ) , ( ( Perl5Compiler . MULTILINE_MASK ) | ( Perl5Compiler . READ_ONLY_MASK ) ) ) ; <END_BUG> } public String getArgumentName ( ) { } public void setPathExtension ( boolean pathExt ) { } public void setPathExtensionNoEquals ( boolean pathExtNoEquals ) { } public void setPathExtensionNoQuestionmark ( boolean pathExtNoQuestionmark ) { } public void setShouldCache ( boolean b ) { } public boolean isPathExtension ( ) { } public boolean isPathExtensionNoEquals ( ) { } public boolean isPathExtensionNoQuestionmark ( ) { } public boolean shouldCache ( ) { } }

Fix:
parameterRegexp = JMeterUtils . getPatternCache ( ) . getPattern ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( "[;\\?&]" + quotedArg ) + "=([^\"\'>&\\s;\\\\]*)[&\\s\"\'>;]?$?" ) + "|\\s[Nn][Aa][Mm][Ee]\\s*=\\s*[\"\']" ) + quotedArg ) + "[\"\']" ) + "[^>]*" ) + "\\s[vV][Aa][Ll][Uu][Ee]\\s*=\\s*[\"\']" ) + "([^\"\']*)" ) + "[\"\']" ) + "|\\s[vV][Aa][Ll][Uu][Ee]\\s*=\\s*[\"\']" ) + "([^\"\']*)" ) + "[\"\']" ) + "[^>]*" ) + "\\s[Nn][Aa][Mm][Ee]\\s*=\\s*[\"\']" ) + quotedArg ) + "[\"\']" ) , ( ( Perl5Compiler . MULTILINE_MASK ) | ( Perl5Compiler . READ_ONLY_MASK ) ) ) ;